柱体自由扭转时的最优横截面形式

当柱体自由扭转时，柱体的抗扭性能与横截面形式有关，针对单连通域下的具有最优抗扭性能的横截面形式问题，本文建立了相应的最优形式控制模型，并通过变分法求解得到：在横截面面积相等的情况下，圆截面是所有截面中使结构整体应变能最小和扭转刚度最大的截面形式，这与圣维南所给的一般性结论是一致的。     

锻造钢锭

<正>为了降低轴外偏析发展程度和减少废品,本文提出一种具有椭圆形横截面的钢锭。钢锭     

东丽推出新型横截面聚酯纤维

聚酯纤维生产商东丽公司开发了一种新型聚酯长丝“Sillook Lafuel”，产品光泽好，手感柔软。sillook Lafuel纤维是对每根长丝表面光的反射角度进行精确分析而制成的。受纤维素纤维结构的启发，东丽公司应用特殊有光聚合物生产出横截面上具有8个椭圆叶型的纤维。该纤维具有如下特性：     

论晚清短篇小说的结构类型

晚清小说是中国小说从传统向现代转换过程中的重要环节。晚清短篇小说的结构既有对小说传统的继承,又开始出现新变。中国传统小说侧重以情节为中心,重视故事的完整性。受此影响,晚清短篇小说往往呈现出"压缩式的长篇"的纵向结构。另一方面,晚清西学东渐,域外小说的大量译介又深刻影响了小说艺术的发展。一些晚清短篇小说不再重视故事的始终,而是聚焦于生活中的某个特定片段,出现了横截面式的小说结构。     

Process of back pressure deep drawing with solid granule medium on sheet metal

The experimental die apparatus of the solid granules medium forming on sheet metal was designed and manufactured.Typical parts,such as conical,parabolic,cylindrical and square-box-shaped components,were successfully trial-produced as well.According to the analysis of the changing trends of the cross-section shape and the wall thickness during the process,it can be found that the shape of the free deformation zone of the sheet metal,which is the most critical thinning area,can be described as an approximately spherical cap.According to this forming feature,back pressure deep drawing technology with solid granules medium on sheet metal was proposed to restrain drastic thinning at the bottom of the part through the joint friction effect of solid granules medium,the back pressure tringle and the sheet metal.Therefore,the deep drawing limit of the sheet metal is significantly improved.In order to fabricate thin-walled rotary parts with great drawing ratio and complex cross-sections,a finite element model based on the material property test of the solid granules medium was established to optimize the scheme of the back pressure deep drawing.The effects on the forming performance of sheet metal from back pressure load and the approach of blank holding control were analyzed through this model.     

Estimating extreme temperature differences in steel box girder using long-term measurement data

The extreme temperature differences in fiat steel box girder of a cable-stayed bridge were studied.Firstly,by using the long-term measurement data collected by the structural health monitoring system installed on the Runyang Cable-stayed Bridge,the daily variations as well as seasonal ones of measured temperature differences in the box girder cross-section area were summarized.The probability distribution models of temperature differences were further established and the extreme temperature differences were estimated with a return period of 100 years.Finally,the temperature difference models in cross-section area were proposed for bridge thermal design.The results show that horizontal temperature differences in top plate and vertical temperature differences between top plate and bottom plate are considerable.All the positive and negative temperature differences can be described by the weighted sum of two Weibull distributions.The maximum positive and negative horizontal temperature differences in top plate are 10.30 ℃ and -13.80 ℃,respectively.And the maximum positive and negative vertical temperature differences between top plate and bottom plate are 17.30 ℃ and-3.70 ℃,respectively.For bridge thermal design,there are two vertical temperature difference models between top plate and bottom plate,and six horizontal temperature difference models in top plate.     

Scattering wave field around a cavity with circular cross-section embedded in saturated soil using boundary element method

Based on Biot＇s theory and considering the properties of a cavity, the boundary integral equations for the numerical simulation of wave scattering around a cavity with a circular cross-section embedded in saturated soil are obtained using integral transform methods. The Cauchy type singularity of the boundary integral equation is discussed. The effectiveness of the properties of soil mass and incident field on the dynamic stress concentration and pore pressure concentration around a cavity is analyzed. Our results are in good agreement with the existing solution. The numerical results of this work show that the dynamic stress concentration and pore pressure concentration are influenced by the degree of fluid-solid coupling as well as the pore compressibility and water permeability of saturated soil. With increased degree of fluid-solid coupling, the dynamic stress concentration improves from 1.87 to 3.42 and the scattering becomes more significant. With decreased index of soil mass compressibility, the dynamic stress concentration increases and its maximum reaches 3.67. The dynamic stress concentration increases from 1.64 to 3.49 and pore pressure concentration improves from 0.18 to 0.46 with decreased water permeability of saturated soil.